Handling Bituminous Crude Oil in Tank Cars

ABSTRACT

Bituminous heavy crude oil is kept at elevated temperatures in order to flow and may be transported in one direction, and light hydrocarbons typically comprising of mixtures of components of which the majority will have molecular chain lengths of 2 to 12 carbon atoms, such as Natural Gas Liquids (NGL), light naphtha, natural gasoline and natural gas condensates may be transported in the opposite direction.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of U.S. patent application Ser. No. 13/869,258 filed Apr. 24, 2013, hereby expressly incorporated by reference herein.

BACKGROUND

This relates to rail tank cars carrying heated heavy oils or bitumen.

Currently, when heavy Canadian crude oil is transported by rail to terminals or refineries in the U.S., the cars are sent back empty. At the same time, large quantities of light hydrocarbons such as condensate and naphtha travel north from the U.S. to the western Canada producers of the heavy oil to be used as diluent so that bitumen can be reduced in viscosity to a point where it can flow in a pipeline at ambient temperatures. At present, the empty railcars are, for the most part, not returned loaded with light hydrocarbons because it takes a long time for the insulated cars to cool down before they can be safely loaded with light hydrocarbons, which means that they either would have to be removed off-site or take up precious space inside terminals or refineries.

Currently, large quantities of bitumen are produced from tar sands either through surface mining or by steam assisted gravity drainage, notably in Alberta, Canada. At ambient temperatures, the viscosity of the bitumen thus produced is too high to allow transportation by pipeline or other conventional means of transportation such as unheated tank trucks, railcars or vessels. Therefore the bitumen is brought to distant markets either after conversion to lighter synthetic crude oil or after dilution with synthetic crude oil but more commonly with light hydrocarbon fractions, usually natural gas condensates or light naphtha, to a viscosity that allows conventional handling methods at ambient temperatures. The conversion to synthetic crude oil and the dilution with light hydrocarbon fractions are costly processes that result in end products that have properties that are less desirable and lead to yield losses and additional processing costs in refineries when compared to mixtures of conventional crude oil and undiluted bitumen.

It is in principle possible to transport undiluted bitumen in insulated railcars over great distances with only minimal heat loss, so that even after 5 to 7 days, the time required to bring a dedicated train of 100 or more railcars (referred to in the industry as “unit trains”) from the principal producing regions in Alberta, Canada, to major refining centers such as the US Gulf Coast, the bitumen is still hot enough to be discharged in liquid form. Even with longer transit times, only minimal heating is necessary to be able to empty the rail car, with heat provided usually in the form of steam supplied to coils attached to the outside of the shell of the rail tank car. The overall economics of transport of undiluted bitumen by rail compare very favorably with the transport of diluted bitumen by pipeline, because of savings in transportation cost of the diluent, and the cost of the diluent itself. The advantage of transportation by rail and the overall energy efficiency of the process can be further enhanced by loading the railcars with a light hydrocarbon liquid as a backhaul cargo to be used as a diluent in the transportation of additional bitumen by pipeline. Overall, there is a shortage of suitable diluents in the bitumen producing regions, while there is an increasing excess of light hydrocarbons in the US as a result of increased natural gas production.

Typically, a rail tank car must be cooled down first before the light hydrocarbons can be loaded in order to avoid the flashing off of flammable hydrocarbon vapors. Even though precautions are taken such as providing electrical grounding to the rail car, it is generally not considered a safe practice to have rapid flow and turbulence in the vapor space when passing through the range of concentrations where the flammable vapors go from too lean for ignition to too rich, especially when the walls of the tank car can be coated by a film of bitumen which would nullify the electrical grounding of the car. This risk can be avoided by cooling down the cars first and/or purging with inert gas, but this adds significantly to the turnaround time of the railcars, which translates into a considerable expense as well as space requirements for the parked rail tank cars. In addition, there are the costs of the inert gas used to purge the car and the losses of hydrocarbon vapor contained in the purged gas, which in dilute form are difficult to recover.

When light hydrocarbon liquids are transported back to locations where bituminous crude oil is produced, additional measures may be required in order to enable the reuse the light hydrocarbon. For instance, the light hydrocarbons will dissolve any residual bituminous crude oil left in the rail car when the light hydrocarbons were loaded. This residual bituminous crude oil may contain asphaltenes, which may precipitate out of the solution. It may therefore be necessary to filter the light hydrocarbon liquids at the receiving terminal, using filters capable of retaining solids in the range of 5 to 10 microns.

Similarly, undiluted bitumen may not be readily available at the rail loading terminal. Most bituminous crude oil is transported to the rail head on gathering pipelines, which requires blending it with in the order of 30% diluent. Also, mined bitumen will contain some diluents used in the extraction process. The diluent already contained in the bituminous crude when it arrives at the rail head by means of a Diluent Recovery Unit, or DRU, which consist essentially of a single atmospheric distillation step, typically operating at temperatures of 120° C. at the top and 200° C. at the bottom of the column.

Although the additional processing steps such as filtration or a DRU require additional capital and operating expenses, the overall cost savings of transporting undiluted bitumen are such that there are still very significant resulting economic benefits.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are described with respect to the following figures:

FIG. 1 is a schematic depiction of a series of rail tank cars loaded with bitumen at elevated temperatures, which may represent part of a unit train of over 100 similar cars, shortly after arrival at its destination;

FIG. 2 shows the same rail cars after unloading now being reloaded with light hydrocarbon liquids;

FIG. 3 shows the predicted offloading rate and time to empty for a rail car loaded with bituminous crude oil when assisted by light hydrocarbon vapors under slight overpressure;

FIG. 4 shows the predicted cooling down profile for a rail car that has been emptied from bituminous crude oil, is under light hydrocarbon vapors, as light hydrocarbon vapors are introduced; and

FIG. 5 is a front elevational view of a rail car according to one embodiment.

DETAILED DESCRIPTION

Bituminous heavy crude oil is kept at elevated temperatures in a range of 80 to 120° C. (180 to 250° F.) in order to flow and may be transported in one direction by rail, and light hydrocarbons may be transported in the opposite direction. The latter comprise mixtures of components with the majority having molecular chain lengths of 2 to 12 carbon atoms including pentanes and hexanes. Examples are light naphtha, natural gasoline and natural gas condensates.

In a first embodiment, heavy bitumen is transported in standard rail tank cars. The rail tank car is insulated with suitable, industry standard insulation materials, such as fiberglass, mineral wool or foam, usually in thicknesses in the order of 10 cm (4 inch) covered with suitable sheeting to prevent ingress of moisture into the insulating material. These cars are also equipped with external heating coils to reheat cars that have cooled down too much during transit to allow efficient offloading of the bitumen.

The rail car is loaded at its origin with bitumen at a suitably high temperature, i.e., in a range of 90 to 120° C. (190 to 200° F.) in order to arrive at its destination after a journey that may take up to 10 days, at temperatures in a range of 70 to 90° C. (160 to 190° F.), at which temperatures the bitumen typically will have a dynamic viscosity in the order of 1,000 to 200 mPa·s.

The rail tank car has connections for transfer of liquid and vapor as per industry standards, typically a 3″ liquid connection at the bottom and a 2″ vapor connection at the top. At its destination, the rail tank car's liquid outlet is connected to a collection system for the bitumen, and the vapor nozzle is connected to a header system that can supply light hydrocarbon vapors under pressure. The pressure of the light hydrocarbon vapors is used to maintain sufficient pressure to displace the bitumen, typically in a range of 50 to 100 kPa gauge (7.5 to 15 psig).

Using light hydrocarbon vapors under slight overpressure considerably speeds up the unloading of the viscous bitumen, and it is possible to offload a 600 bbl cargo in less than two hours versus 4 to 6 hours for unassisted gravity drainage. Also, towards the end of the offloading process, the top layer of the bitumen that then constitutes the heel of the tank, will have absorbed some of the light hydrocarbon vapors. In a typical 25,000 to 30,000 gallon rail car, a 2″ heel represents 90 to 120 gallon (350 to 450 liters) of product. The presence of the light hydrocarbons in the heel improves the final drainage and reduces the amount of heel.

At completion of the discharge of the bitumen, a sensor in the bitumen discharge line will detect the transition from liquid to vapor flow. Several types of detectors are commercially available, including optical, temperature, density and vibration based devices. Given the nature of the service, a vibration-based detector using a single probe is deemed to be the most suitable. At detection of vapor in the discharge line, the signal of the probe may cause a motorized valve in the bitumen discharge line to close, as well as another motorized valve in the line supplying the light hydrocarbon vapors. Process automation steps can be programmed to reopen and close the bitumen discharge valve several times after a short delay, to collect any liquid still left in the car after the first vapor breakthrough. The valve admitting light hydrocarbon vapors can remain closed during these repeated drainage steps.

After the final closure of the valve in the bitumen outlet line, a signal opens a second valve that now connects the vapor space of the tank car to a header that collects vapors and recover the light hydrocarbons in a Vapor Recovery Unit (VRU). VRUs are commonly used in truck, rail and marine loading operations to recover displaced vapors, and are commercially available from multiple vendors. The two main processes practiced in VRUs are cryogenic condensation and absorption/desorption processes using a solvent. The alternative to vapor recovery is vapor destruction, usually through combustion, but that technology is not recommended since initially, concentrations of the light hydrocarbon vapors will be high and recovery will be easy. The recovered light hydrocarbon liquid is led back to the storage tank.

The liquid bitumen is collected in a knockout drum to separate any vapor that broke through before closure of the valve in the liquid discharge line. The vapors are collected and recompressed in order to be condensed in the Vapor Recovery Unit (VRU). The drum can be operated under partial vacuum in order to increase the pressure differential over the bitumen collection header and increase the flow rates for the highly viscous liquid. A level gauge that governs either a variable speed drive on the pump or throttles the flow by means of a control valve in the pump's discharge line controls the bitumen liquid level in the drum. Centrifugal pumps can be used in this service, but positive displacement pumps may be better suited in some embodiments.

After the connection to the bitumen system is closed for the last time, a valve is opened to connect the vapor space to the VRU header through the same flexible hose or loading arm that was used to pressurize the vapor space during the discharge of the bituminous crude oil. A second valve is now opened connecting the flexible hose or loading arm that was used for the discharge of the bitumen, to allow the flow of liquid light hydrocarbons from a common header into the rail tank car. Depending on the composition of the light hydrocarbons and the temperature of the rail tank car after completion of the discharge of bitumen, a certain portion of the light hydrocarbon liquids will vaporize when brought into contact with the still hot tank wall of the rail tank car and the liquid heel of bitumen still remaining at the bottom. Because the tank car at this point is entirely filled with vapors with the same composition as the liquid now entering the rail tank car, the maximum pressure that theoretically can be reached would be the equilibrium pressure of the light hydrocarbons at the temperature of the empty railcar. For light hydrocarbon mixtures consisting primarily of pentanes and hexanes at a temperature of 90° C. (194° F.), the equilibrium pressure would be in a range of 2 to 3 bar gauge (30 to 45 psig), well below the maximum operating pressure of standard rail cars, with is 500 kPa gauge (75 psig) or the safety setting of 600 kPa gauge (90 psig).

Using light hydrocarbon vapors to displace the bitumen therefore creates an intrinsically safe environment for the introduction of the same light hydrocarbons as a liquid: (i) the pressure is limited by the equilibrium pressure of vapor and liquid at the temperatures prevailing in the railcar, which is well below the design pressure of the railcar, and (ii) there is no air present at first introduction and initial vaporization of the light hydrocarbon liquid, and therefore no explosion risk.

The light hydrocarbon vapors resulting from the initial flashing off are vented through the vapor connection of the rail tank car into the same hose or loading arm through which the light hydrocarbon vapors were supplied to displace the bitumen, but now the vapors flow into the header leading to the VRU, where they are easily recovered since they consist almost entirely of hydrocarbon vapors.

The initial vaporization of the light hydrocarbon liquids entering the tank car will last only briefly, typically in the order of 1 to 3 minutes. Thereafter, the sensible heat content of the entering liquid will be sufficient to cool down the incremental area of the shell of the rail tank car covered by the additional liquid and reach an equilibrium temperature well before reaching the boiling point of the liquid at the prevailing pressure.

After the initial flashing off, as cooler liquid light hydrocarbons continue to fill the tank car, the temperature of the liquid will remain below the atmospheric boiling point of the light hydrocarbons despite the heat input from the continued cooling down of the tank car. At this point, below atmospheric pressures might occur. In order to avoid relying on the vacuum relief valves on the tank car to protect the car, a separate vacuum relief valve in the vapor connection to the rail car is provided to admit air and prevent a vacuum. A check valve in the vapor line to the VRU prevents the backflow of vapors from the collection header into the tank car.

Referring to FIG. 1, several rail tank cars 1 are shown that are representative of a larger number, usually up 30 cars per unbroken string, the maximum number being determined by small variations in overall length of the rail cars relative to the fixed positions of offloading and reloading stations along a platform. The cars are all being processed nearly simultaneously, with small differences in timing due to the time required to make the connections, which typically is on the order of 5 minutes per car.

Rail tank car 1 is connected to a collection header 5 for bitumen by means of a flexible hose 2. Alternatively, such a connection can be made using a loading arm. The railcar has either arrived while still sufficiently hot, or has been reheated using steam in the rail cars' heating coils. Ideally, a temperature of 80 to 90° C. (176 to 194° F.) is maintained.

The bitumen discharged from multiple railcars is collected in header 5 and the collective flow, labeled A, is fed into a collection vessel 8, which is centrally located along the loading/unloading platform(s). A second flow of bitumen, also labeled A, flows into vessel 8 from the other side. If the configuration is in multiples of 30 cars per platform, a single vessel could be designed to handle the flows of any multiple of 15 cars simultaneously, being centrally located between parallel tracks. The total stream of bitumen, labeled B, is transferred from vessel 8 to an atmospheric storage tank 11 by means of a pump 9. The level in vessel 8 is maintained by a level controller 10, which controls the variable speed drive of pump 9. Alternatively, a control valve in the discharge line of pump 9 can be used. It is believed that in this service, a variable speed drive and a positive displacement pump are the preferred solution.

The pressure in vessel 8 is maintained by a pressure controller 12, which controls the variable speed drive of a compressor 13. Alternatively, pressure control can be achieved using a control valve or a start-stop cycle. The pressure in vessel 8 can be maintained in this way at a partial vacuum, i.e., in the order of 50 kPa (7.5 psia), which will increase the pressure differential over the collection header and thus increase the flow rate. The compressed vapor stream, labeled C, is fed via a valve 15 and check valve 16 to a Vapor Recovery Unit (VRU) 14 that will recover any condensable hydrocarbons, labeled D, which are run into a storage tank 17 for liquid light hydrocarbons. Non-condensable gases, labeled E, are vented to the atmosphere.

The discharge rate of the rail cars is also increased by pressurizing the cars with light hydrocarbon vapors. This is achieved by means of a pump 18 that draws a stream of liquid light hydrocarbons, labeled F, from storage tank 17 and feeds it into a vaporizer 19. Level in the vaporizer is maintained by level controller 20 acting on valve 21 in the liquid inlet to the vaporizer 19. Pressure in the outlet of the vaporizer 19 is maintained by a pressure controller 22 acting on a flow control valve 23 that regulates the flow of the heat source, labeled G, to the vaporizer. Suitable sources of heat are low-pressure steam, hot water, or thermal oil. The pressure to be maintained is on the order of 50 to 100 kPa gauge (7.5 to 15 psig), which for most light hydrocarbon streams commercially available for this service, such as stabilized condensate or light naphtha, will represent a temperature range of 50 to 70° C. (120 to 160° F.). The vapor stream, labeled H, enters header 27, from which it enters into the top of the rail tank car through valve 28 and a flexible hose 29.

When the rail car is empty, a vapor/liquid interface detector 4, such as a vibration probe, will close valve 3 in the liquid outlet line between the rail car and header 5, and simultaneously close valve 28 to stop any further ingress of light hydrocarbon vapors. Process automation steps can be created to reopen valve 3 after a delay of 2 to 3 minutes to collect any liquids still present in the rail car at the time of first vapor breakthrough. This process can be repeated 2 or 3 times until very little liquid will remain in the rail car.

Any light hydrocarbon vapors that break through prior to closure of valve 3 will be separated from the liquid stream in the knockout drum 8, and sent to the VRU 14 by the compressor 13, to be recycled to the storage tank 17.

Instead of using individual valves 3, 6, 28 and 30, for control of liquid and vapor flows, three-way valves may be used, as known to those skilled in the art. Similarly, the valves or three-way valves may be equipped with limit switches to allow process automation and interlocks to prevent simultaneous opening of valves when only one should be open at the time, such as is the case for valve pairs 3 and 6, and 28 and 30.

Referring to FIG. 2, some of the same cars emptied from bitumen service now are shown being reloaded with light hydrocarbon liquids. Since not all cars are hooked up simultaneously, some cars will be empty and ready for reloading while some, as shown, are still discharging.

After final closure of the bitumen outlet valve 3, the valve 6 is opened, admitting light hydrocarbon liquids from header 26, which is kept at constant pressure by pressure controller 25 acting on flow control valve 24, which regulates the flow from pump 18. The flow rate of liquid light hydrocarbons into the railcar is controlled by flow meter 7 acting on flow control valve 6.

The initial flow of light hydrocarbon liquids entering the rail car 1 will vaporize. Calculations show that under typical conditions, with a 5 cm (2″) heel of bitumen and the shell with the residual contents of the rail car at 90° C. (194° F.), and the light hydrocarbon liquid entering at 30° C. (86° F.), only the first 20 kg (44 lbs) of liquid will vaporize, generating approximately 4 m³ (145 cubic feet) of vapor at 168 kPa (25 psia) and 60° C. (140° F.).

The vapor generated is vented from rail car 1 through hose connection 29 and valve 30 into header 33, from where it is led through valve 34 and check valve 35 into the VRU.

As the rail car fills up, next increments of liquid light hydrocarbons get larger in volume while the incremental wetted surface of hot tank wall these liquid light hydrocarbons come into contact with becomes smaller, at least until the tank is half full. It can be shown that at conditions as described above, i.e., the liquid entering at 30° C. (86° F.), the tank wall being at 90° C. (194° F.), and the vapor initially being at 168 kPa (25 psia) and 60° C. (140° F.), the sensible heat capacity of the liquid is more than enough to cool down the tank wall.

As the temperature in the tank car drops below the atmospheric boiling point for the light hydrocarbon liquid being loaded into the tank car, the pressure may drop to below atmospheric pressure if because the liquids entering the rail tank car 1 are at a temperature below their atmospheric boiling point. In order not to have to rely on the vacuum relief valves of the tank car 1, a vacuum breaker 32 is provided.

Flow controller 7 is provided with a totalizer and at a predetermined quantity corresponding to the maximum permissible fill level of rail tank car 1. When this quantity is reached, the controller 7 will shut valve 6 in the liquid inlet and 30 in the vapor outlet. The rail tank car 1 is now ready to be disconnected and to depart.

FIG. 3 is a graph with the predicted time for emptying a rail tank car loaded with bitumen.

The calculations for discharging the rail car loaded with bitumen are based on the following assumptions: net cargo 106 m³ (28,000 gallon) bitumen; bulk liquid at 80° C. (176° F.) with a dynamic viscosity of 320 mPas; the rail car has a 3″ outlet and is connected by a 3″ hose; the pressure in the vapor space of the rail car above the liquid bitumen is 168 kPa (25 psia) at 60° C.; and the back pressure in the collection header is 125 kPa (18 psia). These conditions will result in a flow rate starting at 0.017 m³/s (270 gallon/minute) falling to 0.013 m³/s (206 gallon/minute) by the time the car is almost empty, for a total time required to discharge the contents of the car of just under two hours.

FIG. 4 is a graph of the predicted cooling down of a rail car empty from bitumen when back loaded with light hydrocarbon liquids.

The calculation for the cooling down of a rail car empty from bitumen is based on the following assumptions: the steel tank wall of the railcar has a thickness of 11.1 mm ( 7/16″); is at 90° C. (194° F.) at the start of the back fill with light hydrocarbon liquids; there is a 5 cm (2″) heel of bitumen still in the tank car, representing about 0.4 m³ (106 gallon); the bitumen heel is also assumed to be at 90° C. (194° F.); and the initial conditions in the vapor space are assumed to be 168 kPa (25 psia) and 60° C. (140° F.). The light hydrocarbon liquid is assumed to consist primarily of pentane and hexane fractions, with a heat of vaporization of 340 kJ/kg (146 Btu/lbs) and a heat capacity of 2.18 kJ/kg·K (0.52 Btu/lbs·R), being introduced at an initial temperature of 30° C. (86° F.), at a constant flow rate of 0.015 m³/s (240 gallon/minute). The initial flashing is calculated to occur only during the first 52 seconds, when the first 0.8 m³ (210 gallon) of light hydrocarbon liquids enter the car, reaching a fill height of 10 cm (4″), of which half is the bitumen heel of the car. Of this initial quantity of light hydrocarbon liquids, it is expected that only a small fraction, i.e., less than 3% will flash, with the bulk of the cooling absorbed by the sensible heat of the liquid, which is heated up from its entry temperature of 30° C. (86° F.) to the equilibrium temperature of the liquid with its vapor at 60° C. (140° F.).

FIG. 5 shows a railcar 1 that is fitted with external heating coils 2 that are welded to the shell of the tank car. The coils 2 are evenly spaced over the length of the shell and are interconnected at or near the top the rail tank car 1 by means of an inlet header 3 that will allow a heating medium such as steam to enter the header 3 via inlet valve 4 to be evenly distributed across the coils 2. The inlet valve 4 is placed at or near the manhole assembly 5, where customarily all other valves such as inlet, outlet and vent valves and pressure relief valves (not shown) are also located. At or near the bottom of the tank car's shell, a second header 6 is provided to collect the spent heating medium such as condensate. Detail A shows an example of how the coil 8 and header 9 can be welded to the shell 10. Shown is a coil with a semi-circular cross section, but other profiles such as angular, rectangular or full circle tubular profiles will also work. The required cross sectional area will depend on such factors as the spacing of the coils acting as stiffeners, material properties and dimensions of the coils and the shell, calculations that are well defined and known to those skilled in the art.

References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application.

While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention. 

What is claimed is:
 1. A method for changing a rail tank car from transporting heated bituminous crude oil to transporting light hydrocarbons comprising: transporting the bituminous crude oil at a temperature of 70° C. or higher; and discharging bituminous crude oil from a rail car using light hydrocarbon vapor under pressure.
 2. The method of claim 1, whereby, after using light hydrocarbon vapors under pressure to discharge the bituminous crude oil from the rail tank car, refilling the rail tank car with light hydrocarbon liquids of the same or similar composition as the vapors.
 3. The method of claim 2 including controlling the introduction of light hydrocarbon liquids such that the vapor generated by boil-off when these liquids come into contact with the rail tank car and any remaining bitumen liquids, does not cause the pressure in the rail tank car to exceed its design pressure, whereby the initial vaporization of the light hydrocarbons is used to cool down the rail tank car and its contents.
 4. The method of claim 1 including emptying multiple rail tank cars simultaneously, with the liquid bituminous crude oil being collected in a common header and led to a collection vessel that is kept under low pressure or partial vacuum by a compressor or vacuum pump in order to assist the viscous flow of the bituminous crude oil.
 5. The method of claim 2 including pumping the light hydrocarbon vapors, drawing light hydrocarbon liquids from a storage tank, to feed said liquids into a vaporizer where external heat is supplied feeding the generated vapors into a common header that allows connection to multiple rail cars simultaneously.
 6. The method of claim 2 including transferring the bituminous crude oil, after separation of entrained vapors in the collection drum, from the collection drum to an atmospheric storage tank without risk of a vapor breakthrough leading to emissions of light hydrocarbons from the atmospheric storage tank.
 7. The method of claim 4 including detecting vapor in the liquid discharge line from the rail car and closing a valve located in said liquid discharge line when a transition from liquid to vapor flow is detected.
 8. The method of claim 7 including reopening and reclosing the valve in the liquid discharge line, in order to collect any liquids still present in the rail tank car at the time of first vapor breakthrough.
 9. The method of claim 8 including opening a flow control valve to admit light hydrocarbon liquids into the rail car.
 10. The method of claim 9 including generating vapors by flashing of light hydrocarbon liquids in contact with the rail tank car and any residual contents in the car, and collecting the vapors displaced by the liquid entering the rail tank car
 11. The method of claim 9 when the temperature of the contents of the car fall below the atmospheric boiling point of the liquid, introducing air into the vapor space, while preventing back-flow of vapors.
 12. The method of claim 1 including handling multiple rail tank cars simultaneously with some cars still being emptied from bituminous crude oil, while others are already in the process of being back filled with light hydrocarbon vapors.
 13. The method of claim 12 including using four separate common headers to allow connection of multiple railcars simultaneously to a bituminous discharge system and a light hydrocarbon liquids system and using a separate pressurized vapor header and a vapor recovery header connected to the vapor space of a rail tank car.
 14. The method of claim 1 including providing the rail car with external coils that allow the transfer of heat from a suitable heating medium to reheat the bitumen, said coils acting as external stiffeners to enable the rail tank car to withstand full internal vacuum. 